A natural grass turf covering has traditionally been cultivated on most playing areas for athletic games. Grass is considered highly desirable both because it stabilizes the soil thereby limiting problems with mud or dust and also because of its attractive appearance. However, maintenance of natural grass turf on athletic playing areas is very expensive at best and is practically impossible on areas subjected to continuous heavy usage.
In order to minimize the expense of maintaining athletic playing areas as well as to increase the durability of the playing surfaces, attempts have been made to substitute synthetic turf for natural turf. However, the results of prior efforts have left much to be desired. Particularly severe problems arise, for example, in the construction of golf greens.
A good golf green must facilitate two types of shots. The first is the approach shot in which a golfer hits the ball from the fairway through the air onto the green. The second is the putt in which the golfer knocks the ball so that it rolls across the green into the cup.
On natural turfs, a good golfer can manage his approach shot onto the green in such a way that the bounce of the ball is limited and the ball does not move unreasonably far from the point of initial impact. In an effort to achieve some degree of resilience, some prior art synthetic turfs have incorporated an elastomeric foam underlay or backing similar to a carpet pad. Synthetic turfs with foam backing are typlified by the materials in Faria, U.S. Pat. No. 3,332,828 and Spinney, U.S. Pat. No. 3,661,687. When such materials are used for golf greens, and an approach shot is made onto the green, the ball generally bounces abnormally and uncontrollably so that it is not possible for even the best of golfers to properly manage his approach shot. Often the ball will keep on bouncing out of control until it bounces right off the green.
Moreover, when a ball is putted on greens made of such synthetic turfs, the grain of the pile fabric, which is inherent in all such materials, affects the direction or course of motion of the ball in an unnatural manner. Consequently, such materials do not provide true putting or chipping surfaces.
Additional problems in putting arise with such surfaces in that they provide too much or too little resistance of the motion of a ball rolling across the surface. When the surface provides too much resistance to the motion of the ball, it is said to be a slow surface. A surface which provides too little resistance to the motion of the ball is termed a fast surface.
Improved artificial playing surfaces for athletic games are disclosed in my prior U.S. Pat. Nos. 3,995,079 and 4,044,179. The '079 patent discloses golf greens formed from a turf-like pile fabric top dressed with noncompacting granular material such as granulated coal slag, crushed flint or crushed granite. Such golf greens do enable a golfer to manage his approach shot onto the green properly, but the top dressing materials generally are not readily available. Consequently, undesirable expense and difficulty may be encountered in installing such a green. It would be desirable if a satisfactory green could be produced by top dressing the green with a commonly available material such as sand. Sand, however, has been found to compact to form a dense hard layer which does not provide the needed shock absorbing characteristics for a golf green. My U.S. Pat. No. 4,044,179 shows a playing surface for athletic games comprising a pile fabric with piles resembling grass disposed upon a firm, stable subsurface and top dressed with sand containing a small amount of moisture modifying material. The sand top dressing compacts to form a dense, hard layer. This type of surface is well suited for tennis courts and also can be used for baseball, soccer and other games. Surfaces of this type are not entirely satisfactory for use as golf greens because the compaction of the top dressing limits the shock absorbing ability of the surface thereby making it difficult for a golfer to properly manage his approach shot onto the green.